1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device which reduces the number of masks and improves an aperture ratio, and a method for fabricating the same.
2. Discussion of the Related Art
As an information-oriented age has been developed, various requirements of display devices have been gradually increased, and in order to satisfy such increase, various flat display devices, such as liquid crystal display devices (LCDs), plasma display panels (PDPs), electro luminescent displays (ELDs), vacuum fluorescent displays (VFDs), etc., have been researched and some of these flat display devices are used now as display devices in various equipments.
From among the above flat display devices, liquid crystal display devices have been mostly used as mobile image display devices while replacing conventional cathode ray tubes (CRT) due to characteristics and advantages thereof, such as excellent image quality, light weight, thin profile and low power consumption, and have been developed as TVs and monitors of computers receiving a broadcast signal and displaying an image in addition to a mobile purpose, such as monitors of notebook computers.
Such a liquid crystal display device includes a color filter substrate on which a color filter array is formed, a thin film transistor substrate on which a thin film transistor array is formed, and a liquid crystal layer formed between the color filter substrate and the thin film transistor substrate.
As representative driving modes which are mostly used in liquid crystal display devices, there are a twisted-nematic (TN) mode in which liquid crystal directors are aligned to be twisted at an angle of 90° and are driven by applying voltage thereto, and an in-plane switching (IPS) mode in which liquid crystals are driven by a horizontal electric field between pixel electrodes and common electrodes aligned in parallel on one substrate.
In the IPS mode, pixel electrodes and common electrodes are alternately formed at an opening of a thin film transistor substrate, and liquid crystals are aligned by a horizontal electric field generated between the pixel electrodes and the common electrodes. An IPS mode liquid crystal display device has a wide viewing angle but has a low aperture ratio and low transmittance, and thus in order to improve such problems, a fringe field switching (FFS) mode liquid crystal display device has been proposed.
The FFS mode liquid crystal display device includes a common electrode of a single electrode shape formed at a pixel part and a plurality of pixel electrodes of slit shapes formed on the common electrode, or includes a pixel electrode of a single electrode shape and a plurality of common electrodes of slit shapes, thus operating liquid crystal molecules by a fringe field formed between the pixel and common electrodes.
Hereinafter, with reference to FIG. 1, a method for fabricating a general FFS mode liquid crystal display device will be described.
FIG. 1 is a cross-sectional view of a general liquid crystal display device.
With reference to FIG. 1, the method for fabricating the general FFS mode liquid crystal display device includes forming gate lines (not shown), gate electrodes 10a, gate pad lower electrodes (not shown), data pad lower electrodes (not shown) and common lines (not shown) on a lower substrate 10 using a first mask, forming a semiconductor layer 13 including an active layer 13a and an ohmic contact layer 13b using a second mask, forming source and drain electrodes 14a and 14b and data lines DL using a third mask, and forming first and second passivation films 15a and 15b having pixel contact holes, gate contact holes and data contact holes using a fourth mask.
The method for fabricating the general FFS mode liquid crystal display device further includes forming pixel electrodes 16 provided on the second passivation film 15b and connected to the drain electrodes 14b using a fifth mask, forming a third passivation film 15c exposing the gate pad lower electrodes (not shown) and the data pad lower electrodes (not shown) using a sixth mask, and forming common electrodes 17 generating a fringe field with the pixel electrodes 16 such that the third passivation film 15c is interposed between the common electrodes 17 and the pixel electrodes 16, gate pad upper electrodes (not shown) connected to the gate pad lower electrodes (not shown) and data pad upper electrodes (not shown) connected to the data pad lower electrodes (not shown) using a seventh mask.
The method for fabricating the general FFS mode liquid crystal display device further includes forming R, G and B color filters (not shown) and a black matrix 19 on an upper surface 20, and forming column spacers (not shown) to maintain a cell gap between the lower substrate 10 and the upper substrate 20, and thus the general liquid crystal display device is formed using 12 or more masks. Therefore, the fabricating process of the general liquid crystal display device is complicated and the manufacturing cost of the general liquid crystal display device is increased.